This document relates to coding for visual prostheses.
According to the World Health Organization, in 2002 more than 161 million people were visually impaired, of whom 124 million had low vision and 37 million were blind. Moreover, blindness has been estimated to cost the US federal government alone $4 billion a year. An artificial vision system is expected to have a huge impact on society and preliminary results with visual prosthesis devices now under development are very encouraging.
Neural tissue can be stimulated by pulses of electrical current through electrodes. Visual sensation can be created by stimulating neural tissues used during visual processing. Currently, the four main approaches to visual prosthesis involve cortical implants, retinal implants, optic nerve cuff electrodes, and dorsal lateral geniculate nucleus (LGN) implants. The last approach has been proposed recently, and preliminary results suggest that this approach has great promise. In this kind of implant, electrodes directly stimulate the LGN, which is the part of the thalamus that relays signals from the retina to the primary visual cortex (also known as V1).
The visual information, which may be obtained using a camera, can be coded in electrical pulses, which are relayed to the nervous system via the electrodes of the prosthetic device. It has been shown that an image with a 25×25 array of pixels allows suitable face recognition, mobility, and reading speed. However, only a much smaller number of electrodes is currently available in state-of-the-art prostheses.